Field of the Invention
The present invention relates to a catalytic converter for cleaning exhaust gas, including a converter housing and at least one honeycomb body disposed therein and containing layers of sheet metal having catalytically active material. The converter is disposed on a dividing wall of a muffler housing for a small engine, the dividing wall has at least one opening, and the housing has an upper housing component and a lower housing component.
As environmental consciousness has become stronger and exhaust gas regulations relating to the exhaust gases of internal combustion engines have become stricter, a need has arisen to provide catalytic exhaust gas cleaning in small engines. Small engines are understood below to be internal-combustion engines with an engine capacity of less than 200 cm.sup.3, in particular less than 50 cm.sup.3. Such engines are found, in particular, in lawnmowers, power saws, transportable power packs, two-wheeled vehicles and such applications. In particular, in power saws, lawnmowers and other garden implements driven by internal-combustion engines, someone using such an implement is frequently located directly in the region of the exhaust gases of the small engine over a relatively long period of time. Catalytic exhaust gas cleaning is particularly important for that reason.
European Patent 0 470 113 B1 discloses a metallic catalytic converter carrier body which is suitable in particular for attachment in the dividing wall of a muffler housing. However, the construction and type of configuration of that catalytic converter carrier body are not very well suited to many muffler configurations. In addition, the manufacture thereof involves a certain degree of complexity.
The exhaust gas which enters a muffler near to the engine is, as a rule, already at a high temperature of, for example, over 600.degree. C. As a result of exothermal reactions in the catalytic converter, its temperature may also rise considerably, for example to 1000.degree. C. German Published, Non-Prosecuted Patent Application DE 38 29 668 A1, corresponding to U.S. Pat. No. 4,867,270, discloses a protection mechanism for an exhaust gas muffler for two-stroke engines, in particular for portable implements such as power saws or the like, having a housing, a catalytic converter and an exhaust gas end pipe. The catalytic converter is disposed in a hollow body which is provided in the muffler housing with spacing on all sides and has an output with a tapering cross section in the direction of flow of the treated exhaust gas that leads the treated exhaust gas out of the housing. The mechanical structure of that exhaust gas muffler is very complex and requires a specifically constructed adaptation of the catalytic converter for the respective purpose of use. Furthermore, the exhaust gas muffler has a large volume.
The above-described configurations for the catalytic exhaust gas cleaning of small engines additionally require specially fabricated honeycomb bodies. The manufacture, catalytic coating and installation of those honeycomb bodies require a relatively large number of working steps and are therefore relatively expensive in comparison with equipment provided with a small engine. For that reason, the provision of a catalytic converter for a small engine is frequently dispensed with.